Referring to FIGS. 1 and 2, an extendable worktable 1 is shown used in a machine for carrying a workpiece (not shown). The extendable worktable 1 includes a body 11, two extension members 12 arranged at two opposite sides relative to the body 11 and movable toward or away from the body 11. Four guide rods 13 are respectively connected to the extension members 12 and are mounted into the bottom side of the body 11 and are movable with the extension members 12 relative to the body 11. Four clamps 14 located on the bottom side of the body 11 and are respectively attached to the guide rods 13, and four locking levers 15 are respectively coupled to the clamps 14 and are operable to move the clamps 14 between a locking position, where the clamps 14 lock the respective guide rods 13 from moving relative to the worktable body 11, and an unlocking position, where the clamps 14 allow the guide rods 13 to move with the extension members 12 relative to the body 11 to accommodate different sized workpieces on the worktable 1.
However, in order to move the extension members 12, it is necessary to first operate the locking levers 15 for enabling the clamps 14 to release the respective guide rods 13, and then to move the extension members 12 relative to the body 11, and then to operate the locking members 15 to lock the guide rods 13 from further movement. This manner of operating the extendable worktable 1 is inconvenient.